Recording with your iPhone's built-in microphone is a quick and easy way for musicians to sketch out song ideas. To take the iPhone's audio-recording capabilities to the next level, you'll need to drop some money on a quality recording app, and some kind of adapter for connecting instruments or mixers.
Fortunately, the folks at Sonoma Wire Works have created the best solution we've seen yet. The GuitarJack ($199) plugs into the dock connection of your iPhone or iPod Touch (though the latest iPhone and iPod models aren't supported) and bestows them with a 1/4-inch instrument input, stereo line input, and headphone output.
Unlike some of the guitar-specific or mic-specific accessories we've tested in the past (such as Mikey or AmpliTube iRig), GuitarJack distinguishes itself with a uniquely durable aluminum construction and a Switchcraft instrument jack made from a nickel-plated brass.
The left side of the GuitarJack includes a headphone output and stereo minijack input that can be adjusted to accept hi-z or low-z impedance for use with microphones or line level input. A metal emblem for Sonoma Wire Works is also here, but offers no function beyond looking pretty. A 1/4-inch input is located on the opposite edge; it can also be adjusted for high or low gain input. As the name implies, this input is intended primarily for use with guitar, but can also be adjusted for use with keyboards or microphones.